1. Field of the Invention
The present invention relates to a computerized method for tomographic image exposure and reconstruction.
2. Description of the Related Art
Computed tomography involves a first step of acquiring X-ray projection images (also called X-ray projections) by irradiating a patient or an object with an X-ray beam emitted in different directions and detecting the X-ray projection images by means of a radiation detector and generating a digital representation of these projection images.
A 3D image of the patient is then computed by applying a tomographic reconstruction algorithm to the acquired digital X-ray projection images.
The multitude of X-ray projection images that are required for tomographic image reconstruction can be acquired in different ways.
In a first method referred to as step-and-shoot protocol, an X-ray tube and radiation detector are stationary and move to a next location only in between exposures. While this protocol is the easiest from an image reconstruction point of view, it poses severe constraints on the design of the modality and typically leads to longer acquisition times.
An alternative acquisition strategy is to keep the X-ray source in a constant motion, the so called continuous acquisition mode. When conventional reconstruction algorithms are applied, the inherent angular integration of the beams during exposure causes blurring in the reconstructed images. Typically, this is considered an unwanted side effect of this acquisition mode and therefore the acquisition protocol is designed to limit the angular beam integration as much as possible. In a spiral CT scanner for example, the constant motion of the X-ray tube and the table enables a heavily reduced acquisition time compared to the original step-and-shoot modality, while a high number of projections reduces the angle of integration and limits the blurring in the reconstructed images.
In more recent tomosynthesis and cone-beam CT systems, a flat panel detector is used to capture the X-rays. Compared to CT scanners, these detectors are typically slower and acquisitions are made with a flashing X-ray source, which rotates slowly and radiates the subject at specified intervals. The constantly moving tube in continuous acquisition mode also allows a shorter acquisition time, at the cost of a slightly reduced resolution with step-and-shoot reconstruction algorithms, caused by the angular integration of the beams during the X-ray flashes. The angle of integration during a projection is limited by a short exposure time and low rotation speed.
It is an object of this invention to improve the reconstruction image quality.
In the publication by Michielsen Koen et al: “Patchwork reconstruction with resolution modeling for digital breast tomosynthesis”, Medical Physics, AIP, Melville, N.Y., US, vol. 40, no. 3, a computerized tomographic image exposure and reconstruction method is disclosed wherein an object is subjected to irradiation during a relative movement of a source of radiation, said object and a radiation detector and wherein a digital representation of the radiation image of said object is computed by applying a tomographic reconstruction algorithm to image data read out of the irradiated radiation detector. A number of projection images are generated and are modeled into a tomographic reconstruction algorithm.